1. Field of the Invention
The present invention relates to an integrated semiconductor optical device and an optical apparatus using the same.
2. Description of the Related Art
Japanese Unexamined Patent Application Publication No. 64-28984 discloses an integrated semiconductor optical device. The integrated semiconductor optical device includes a distributed feedback laser diode (DFB laser diode), an optical modulator, and a connected portion provided between the DFB laser diode and the optical modulator. The connected portion is made of high-resistance semiconductor material.
Japanese Unexamined Patent Application Publication No. 8-335745 discloses a semiconductor light emitting device. The semiconductor light emitting device includes a distributed feedback laser diode portion (or DFB laser diode portion), an optical modulator portion, and an isolation portion provided between the DFB laser diode portion and the optical modulator portion. The method for manufacturing the semiconductor light emitting device includes the following steps. Firstly, an optical guiding layer made of n type InGaAsP is grown on n-type InP substrate. An active layer with multi quantum well (MQW) structure is grown on the DFB laser diode portion of the optical guiding layer, and an optical absorption layer with MQW structure is grown on the isolation portion and the optical modulator portion of the optical guiding layer. Then, a separate confinement heterostructure (SCH) layer made of p type InGaAsP, a cladding layer made of p type InP, and a contact layer made of p type InGaAsP are grown on the active layer and the optical absorption layer. Subsequently, any of Zn, Cu, proton and Fe is injected into the isolation portion between the DFB laser diode portion and the optical modulator portion to form a non-radiative recombination center that reaches an optical waveguide region. In this process, disordering occurs in the MQW structure of the optical absorption layer of the isolation portion. Consequently, band of absorption wavelength is shifted toward a shorter wavelength and absorption of laser beam is reduced, accordingly.
Japanese Unexamined Patent Application Publication No. 2000-501238 discloses a low resistance contact semiconductor diode. In the semiconductor laser, a layer of heavily doped p-type semiconductor material is replaced by a layer of heavily doped n-type semiconductor material and a thin layer of heavily doped p-type semiconductor material. This structure facilitates low resistance contact.
Elec. Lett. 39(2003) Vol. 39 No. 5 pp. 437, Electron Letters Online No. 20030288 discloses a vertical-cavity surface emitting-layer (VCSEL) using AlGaInAs/AlGaInAs tunnel junction.
Jpn. J. Appl. Phys Vol. 39 (2000) pp. 1727-1729 discloses a vertical-cavity surface emitting-layer (VCSEL) using p+InGa(Al)As/n+InGa(Al)As tunnel junction.
In an integrated semiconductor optical device including a plurality of semiconductor optical devices formed on a substrate, one semiconductor optical device and another semiconductor optical device are coupled optically to each other. These semiconductor optical devices are separated electrically from each other. These semiconductor optical devices are formed by layering an n-type cladding layer, an active layer and a p-type cladding layer in this order on the semiconductor substrate. The active layer is located between the n-type cladding layer and the p-type cladding layer and has a pin structure. When the active layer is forward biased, the semiconductor optical device operates as a light emitting device. When the active layer is reverse biased, the semiconductor optical device operates as an optical photodiode or an optical modulation device.
The integrated device described in Japanese Unexamined Patent Application Publications No. 64-28984 and No. 8-335745 includes two types of semiconductor optical device, that is, a semiconductor laser and an optical modulation device. A semiconductor layer stack for forming the semiconductor laser, and a semiconductor layer stack for forming the optical modulation device are formed on an n-type semiconductor substrate. The semiconductor layer stack in the semiconductor laser region includes an active layer and a p-type semiconductor layer. The semiconductor layer stack in the optical modulation device region also includes another active layer and another p-type semiconductor layer. A p-side electrode is formed on the p-type semiconductor layer of the semiconductor laser region. Similarly, another p-side electrode is formed on the p-type semiconductor layer of the optical modulation device region. On the other hand, a common n-side electrode is formed on the other side of the n-type semiconductor substrate. The p-side electrodes formed in the semiconductor laser region and the optical modulation device region are insulated electrically from each other.
As a structure for electrical isolation of the two semiconductor optical devices, Japanese Unexamined Patent Application Publication No. 64-28984 discloses an isolation region in which a high-resistance semiconductor is buried and grown. In the isolation region, discontinuity is formed in the waveguide structure during the processes of etching, burying and growing. This discontinuity causes optical scattering loss. In forming the isolation region, the number of processes of crystal growth increases, so that the processes are complicated.
As a structure for electrical isolation of the two semiconductor optical devices, Japanese Unexamined Patent Application Publication No. 8-335745 discloses an isolation region which is different from that of Japanese Unexamined Patent Application Publication No. 64-28984. In the isolation region, a p-type carrier is inactivated. Therefore, value of resistance of the relevant part is high. The inactivation of the carrier is performed by forming crystal defect by implanting proton and/or iron ion into part of a p-type clad. However, since the ion implantation leads defect into the semiconducting crystal, it has been found out that when the isolation region is formed using the ion implantation, reliability of device deteriorates.
Elec. Lett. 39(2003) Vol. 39 No. 5 pp. 437, Electron Letters Online No. 20030288 and Jpn. J. Appl. Phys Vol. 39 (2000) pp. 1727-1729 disclose a VCSEL, which includes a tunnel junction for confining a current into the active region.